The laser Doppler technique is a clinically applicable, noninvasive technique that enables one to obtain measurements of the blood flow rate at selectable sites in the retinal vasculature. It is the only known noninvasive technique that can provide objective, quantitative measurements of retinal blood flow. In addition, it is the only known technique that can measure instantaneous changes in the velocity of red blood cells flowing in individual retinal vessels, a requirement for the complete characterization of retinal hemodynamics. Because of the large energy requirements of the retina as it functions in the visual process, it requires a well-functioning vascular system to provide a sufficient, well-regulated blood supply. The ability of the retinal circulation to autoregulate its blood supply in accordance with its metabolic needs is central to its proper functioning. Several major disease processes with specific retinal complications have been linked to a pathologic functioning of the autoregulatory mechanism. Further improvements in the laser Doppler technique, its application to studies aimed at elucidating the operation of the autoregulatory mechanism, and its application to studies of retinal vascular disease, with emphasis on diagnosis, prognosis, and monitoring the effectiveness of therapeutic interventions, should lead to substantial new information about retinal blood flow and its role in the development of retinal diseases. Accordingly, the specific aims of the proposed research are: (1) to improve the quality of the data as well as the ease of data acquisition by implementing techniques resulting in stabilization of the incident laser beam on the target vessel, (2) to implement a computer-assisted automatic data analysis system featuring the display of results within minutes of data acquisition, (3) to characterize quantitatively the normal human retinal circulation in terms of blood flow, flow pulsatility, and oxygen delivery, (4) to investigate the autoregulatory response of the retinal circulating to local and systemic perturbations, and (5) to characterize quantitatively the retinal circulation of selected patients with diabetic retinopathy, central and branch vein occlusions, myopia, retinal detachment, and carotid artery disease, and to determine the effects of therapeutic interventions in specific cases.